Tracy Kloczynski

β2-Nicotinic Acetylcholine Receptor Availability During Acute and Prolonged Abstinence From Tobacco Smoking

CONTEXT Available levels of nicotinic acetylcholine receptors containing the beta(2) subunit (beta(2)*-nAChR) are higher in recently abstinent tobacco smokers compared with participants who never smoked. Variations in beta(2)*-nAChR availability during the course of abstinence may be related to the urge to smoke, the extent of nicotine withdrawal, and successful abstinence. OBJECTIVE To examine changes in beta(2)*-nAChR availability during acute and prolonged abstinence from tobacco smoking and to determine how changes in beta(2)*-nAChR availability were related to clinical features of tobacco smoking. DESIGN Tobacco smokers participated in up to 4 iodide 123-labeled 5-iodo-A-85380 ([(123)I]5-IA) single-photon emission computed tomography (SPECT) scans during abstinence at 1 day (n = 7) and 1 (n = 17), 2 (n = 7), 4 (n = 11), and 6 to 12 (n = 6) weeks. Age-matched nonsmokers participated in a single [(123)I]5-IA SPECT scan. All participants completed 1 magnetic resonance imaging study. SETTING Academic imaging center. PARTICIPANTS Tobacco smokers (n = 19) and an age-matched nonsmoker comparison group (n = 20). Main Outcome Measure The [(123)I]5-IA SPECT images were converted to distribution volume and were analyzed using regions of interest. RESULTS Compared with nonsmokers, beta(2)*-nAChR availability in the striatum, cortex, and cerebellum of smokers was not different at 1 day of abstinence, was significantly higher at 1 week of abstinence, and was not different at 4 or at 6 to 12 weeks of abstinence. In smokers, beta(2)*-nAChR availability was significantly lower in the cortex and cerebellum at 6 to 12 weeks compared with 1 week of abstinence. In addition, cerebellar beta(2)*-nAChR availability at 4 weeks of abstinence was positively correlated with craving on the day of the SPECT scan. CONCLUSIONS These data suggest that higher beta(2)*-nAChR availability persists up to 1 month of abstinence and normalizes to nonsmoker levels by 6 to 12 weeks of abstinence from tobacco smoking. These marked and persistent changes in beta(2)*-nAChR availability may contribute to difficulties with tobacco cessation.

Endotoxin-induced systemic inflammation activates microglia: [11C]PBR28 positron emission tomography in nonhuman primates

UNLABELLED Microglia play an essential role in many brain diseases. Microglia are activated by local tissue damage or inflammation, but systemic inflammation can also activate microglia. An important clinical question is whether the effects of systemic inflammation on microglia mediate the deleterious effects of systemic inflammation in diseases such as Alzheimers dementia, multiple sclerosis, and stroke. Positron Emission Tomography (PET) imaging with ligands that bind to Translocator Protein (TSPO) can be used to detect activated microglia. The aim of this study was to evaluate whether the effect of systemic inflammation on microglia could be measured with PET imaging in nonhuman primates, using the TSPO ligand [(11)C]PBR28. METHODS Six female baboons (Papio anubis) were scanned before and at 1h and/or 4h and/or 22 h after intravenous administration of E. coli lipopolysaccharide (LPS; 0.1mg/kg), which induces systemic inflammation. Regional time-activity data from regions of interest (ROIs) were fitted to the two-tissue compartmental model, using the metabolite-corrected arterial plasma curve as input function. Total volume of distribution (V(T)) of [(11)C]PBR28 was used as a measure of total ligand binding. The primary outcome was change in V(T) from baseline. Serum levels of tumor necrosis factor alpha (TNFα), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and interleukin-8 (IL-8) were used to assess correlations between systemic inflammation and microglial activation. In one baboon, immunohistochemistry was used to identify cells expressing TSPO. RESULTS LPS administration increased [(11)C]PBR28 binding (F(3,6)=5.1, p=.043) with a 29 ± 16% increase at 1h (n=4) and a 62 ± 34% increase at 4h (n=3) post-LPS. There was a positive correlation between serum IL-1β and IL-6 levels and the increase in [(11)C]PBR28 binding. TSPO immunoreactivity occurred almost exclusively in microglia and rarely in astrocytes. CONCLUSION In the nonhuman-primate brain, LPS-induced systemic inflammation produces a robust increase in the level of TSPO that is readily detected with [(11)C]PBR28 PET. The effect of LPS on [(11)C]PBR28 binding is likely mediated by inflammatory cytokines. Activation of microglia may be a mechanism through which systemic inflammatory processes influence the course of diseases such as Alzheimers, multiple sclerosis, and possibly depression.

Imaging Nicotine- and Amphetamine-Induced Dopamine Release in Rhesus Monkeys with [ 11 C]PHNO vs [ 11 C]raclopride PET

The radiotracer [11C]PHNO may have advantages over other dopamine (DA) D2/D3 receptor ligands because, as an agonist, it measures high-affinity, functionally active D2/D3 receptors, whereas the traditionally used radiotracer [11C]raclopride measures both high- and low-affinity receptors. Our aim was to take advantage of the strength of [11C]PHNO for measuring the small DA signal induced by nicotine, which has been difficult to measure in preclinical and clinical neuroimaging studies. Nicotine- and amphetamine-induced DA release in non-human primates was measured with [11C]PHNO and [11C]raclopride positron emission tomography (PET) imaging. Seven adult rhesus monkeys were imaged on a FOCUS 220 PET scanner after injection of a bolus of [11C]PHNO or [11C]raclopride in three conditions: baseline; preinjection of nicotine (0.1 mg/kg bolus+0.08 mg/kg infusion over 30 min); preinjection of amphetamine (0.4 mg/kg, 5 min before radiotracer injection). DA release was measured as change in binding potential (BPND). Nicotine significantly decreased BPND in the caudate (7±8%), the nucleus accumbens (10±7%), and in the globus pallidus (13±15%) measured with [11C]PHNO, but did not significantly decrease BPND in the putamen or the substantia nigra or in any region when measured with [11C]raclopride. Amphetamine significantly reduced BPND in all regions with both radiotracers. In the striatum, larger amphetamine-induced changes were detected with [11C]PHNO compared with [11C]raclopride (52–64% vs 33–35%, respectively). We confirmed that [11C]PHNO is more sensitive than [11C]raclopride to nicotine- and amphetamine-induced DA release. [11C]PHNO PET may be more sensitive to measuring tobacco smoking-induced DA release in human tobacco smokers.

Assessing the sensitivity of [11C]p943, a novel 5-HTIB radioligand, to endogenous serotonin release

The main objective of the current study was to determine the sensitivity of the positron emission tomography (PET) radioligand [11C]P943 to fenfluramine‐induced changes in endogenous 5‐HT in nonhuman primate brain. Fenfluramine‐induced changes in 5‐HT1B occupancy were compared to those obtained by self‐block with unlabeled P943. Two baboons and 1 rhesus monkey were given preblocking or displacing doses of fenfluramine (1–5 mg/kg) or preblocking doses of unlabeled P943 (0.2 mg/kg) and imaged with [11C]P943 PET. Receptor occupancy by the low dose of fenfluramine (1 mg/kg) in the baboons was 25 and 29% and by the high dose of fenfluramine (5 mg/kg) in the rhesus macaque was 42%. Receptor occupancy by P943 (0.2 mg/kg) was 68 and 86% in the baboons. PET imaging of 5‐HT1B receptors with [11C]P943 may be a useful approach for measuring changes in endogenous 5‐HT in the living human brain. Synapse, 2011.

GABAA-benzodiazepine receptor availability in smokers and nonsmokers: Relationship to subsyndromal anxiety and depression†

Many smokers experience subsyndromal anxiety symptoms while smoking and during acute abstinence, which may contribute to relapse. We hypothesized that cortical gamma aminobutyric acidA‐benzodiazepine receptor (GABAA‐BZR) availability in smokers and nonsmokers might be related to the expression of subsyndromal anxiety, depressive, and pain symptoms. Cortical GABAA‐BZRs were imaged in 15 smokers (8 men and 7 women), and 15 healthy age and sex‐matched nonsmokers, and 4 abstinent tobacco smokers (3 men; 1 woman) using [123I]iomazenil and single photon emission computed tomography (SPECT). Anxiety and depressive symptoms were measured using the Spielbergers State‐Trait Anxiety Index (STAI) and the Center for Epidemiology Scale for Depressive Symptoms (CES‐D). The cold pressor task was administered to assess pain tolerance and sensitivity. The relationship between cortical GABAA‐BZR availability, smoking status, and subsyndromal depression and anxiety symptoms, as well as pain tolerance and sensitivity, were evaluated. Surprisingly, there were no statistically significant differences in overall GABAA‐BZR availability between smokers and nonsmokers or between active and abstinent smokers; however, cortical GABAA‐BZR availability negatively correlated with subsyndromal state anxiety symptoms in nonsmokers but not in smokers. In nonsmokers, the correlation was seen across many brain areas with state anxiety [parietal (r = −0.47, P = 0.03), frontal (r = −0.46, P = 0.03), anterior cingulate (r = −0.47, P = 0.04), temporal (r = −0.47, P = 0.03), occipital (r = −0.43, P = 0.05) cortices, and cerebellum (r = −0.46, P = 0.04)], trait anxiety [parietal (r = −0.72, P = 0.02), frontal (r = −0.72, P = 0.02), and occipital (r = −0.65, P = 0.04) cortices] and depressive symptoms [parietal (r = −0.68; P = 0.02), frontal (r = −0.65; P = 0.03), anterior cingulate (r = −0.61; P = 0.04), and temporal (r = −0.66; P = 0.02) cortices]. The finding that a similar relationship between GABAA‐BZR availability and anxiety symptoms was not observed in smokers suggests that there is a difference in GABAA‐BZR function, but not number, in smokers. Thus, while subsyndromal anxiety and depressive symptoms in nonsmokers may be determined in part by GABAA‐BZR availability, smoking disrupts this relationship. Aberrant regulation of GABAA‐BZR function in vulnerable smokers may explain why some smokers experience subsyndromal anxiety and depression. Synapse 63:1089–1099, 2009.

Brain β2*-nicotinic acetylcholine receptor occupancy after use of a nicotine inhaler

The Nicotrol® (Pfizer, USA) nicotine inhaler reduces craving by mimicking the behavioural component of cigarettes and delivering controlled doses of nicotine, which binds to the beta-2 subunit-containing nicotinic acetylcholine receptors (β2*-nAChRs). Previous studies examined β2*-nAChR occupancy after administration of regular and low-nicotine cigarettes. Here, we measured occupancy of β2*-nAChRs after administration of nicotine via inhaler, and the relationship between occupancy and changes in craving for tobacco smoking and withdrawal symptoms. Tobacco smokers participated in [123I]5-IA-85380 SPECT studies with either a nicotine inhaler (n=9) or tobacco cigarette (n=4) challenge. [123I]5-IA was administered as a bolus plus constant infusion. After equilibrium was achieved, three 30-min baseline scans were collected, and subjects either used the nicotine inhaler or a regular cigarette, and up to six additional scans were obtained. Receptor occupancy was determined based on the Lassen plot method. Craving for tobacco smoking and withdrawal symptoms were evaluated pre- and post-challenge. Use of the nicotine inhaler produced an average 55.9±6.4% occupancy of β2*-nAChRs 2-5 h post-challenge, whereas use of a cigarette produced significantly higher receptor occupancy (F=10.6, p=0.009) with an average 67.6±14.1% occupancy 1.5-5 h post-challenge. There was a significant decrease in withdrawal symptoms post-nicotine inhaler use (F=6.13, p=0.04). These results demonstrate significant differences in occupancy of β2*-nAChRs by nicotine after use of the inhaler vs. a cigarette and confirm the ability of the nicotine inhaler to relieve withdrawal symptoms.

Tobacco smoking interferes with GABAA receptor neuroadaptations during prolonged alcohol withdrawal

Significance Alcohol dependence and tobacco smoking are highly comorbid. Although continued smoking during alcohol withdrawal may reduce relapse risk, most of the morbidity associated with alcohol dependence is due to tobacco smoking and many individuals in alcohol treatment express a desire to quit smoking. We conducted a parallel study in alcohol-dependent humans and nonhuman primates to identify the impact of tobacco smoke and nicotine on the neuroadaptations in the GABA-ergic system that occur during alcohol withdrawal. Our findings show that tobacco smoking, but not nicotine consumption, blocks the recovery of GABAA receptors during extended alcohol withdrawal and that sustained elevations in GABAA receptor levels in alcohol-dependent smokers are associated with alcohol and cigarette cravings, possibly contributing to continued smoking. Understanding the effects of tobacco smoking on neuroadaptations in GABAA receptor levels over alcohol withdrawal will provide critical insights for the treatment of comorbid alcohol and nicotine dependence. We conducted parallel studies in human subjects and nonhuman primates to investigate the differential effects of tobacco smoking and nicotine on changes in GABAA receptor availability during acute and prolonged alcohol withdrawal. We report that alcohol withdrawal with or without concurrent tobacco smoking/nicotine consumption resulted in significant and robust elevations in GABAA receptor levels over the first week of withdrawal. Over prolonged withdrawal, GABAA receptors returned to control levels in alcohol-dependent nonsmokers, but alcohol-dependent smokers had significant and sustained elevations in GABAA receptors that were associated with craving for alcohol and cigarettes. In nonhuman primates, GABAA receptor levels normalized by 1 mo of abstinence in both groups—that is, those that consumed alcohol alone or the combination of alcohol and nicotine. These data suggest that constituents in tobacco smoke other than nicotine block the recovery of GABAA receptor systems during sustained alcohol abstinence, contributing to alcohol relapse and the perpetuation of smoking.

Decreased Beta2*-nicotinic acetylcholine receptor availability after chronic ethanol exposure in nonhuman primates

Ethanol associated behaviors have been linked to the β2‐subunit containing nicotinic acetylcholine receptors (β2*‐nAChR); however, there is conflicting evidence on ethanol‐induced changes in nAChR expression during and after chronic ethanol consumption. In this study, five male animals orally self‐administered ethanol for 18 ± 1 weeks. Animals were scanned with [123I]5‐IA‐85380 and SPECT prior to ethanol self‐administration, and at 24 h and 5‐13 wks withdrawal. β2*‐nAChR availability was not significantly different from baseline at 24 h withdrawal, but was significantly decreased compared to baseline at 5‐13 wks withdrawal throughout the cortex and in the thalamus, but not the midbrain. The percent decrease in β2*‐nAChR availability from baseline to 5‐13 wks withdrawal in the parietal cortex was negatively correlated with total grams of ethanol consumed in lifetime and in the midbrain was negatively correlated with average daily ethanol consumption (g/kg). Prolonged withdrawal from chronic ethanol consumption is associated with a decrease in β2*‐nAChR availability. The decrease in β2*‐nAChR availability is influenced by alcohol consumption, suggesting the chronicity and severity of alcohol consumption may underlie persistent changes in β2*‐nAChR availability. Synapse 64:729–732, 2010.

Evaluation of the sensitivity of the novel α4β2* nicotinic acetylcholine receptor PET radioligand 18F-(−)-NCFHEB to increases in synaptic acetylcholine levels in rhesus monkeys

18F‐(‐)‐NCFHEB (also known as 18F‐(‐)‐Flubatine) is a new radioligand to image α4β2* nicotinic acetylcholine receptors in vivo with positron emission tomography (PET), with faster kinetics than previous radioligands such as 18F‐2‐F‐A85380. The goal of this study was to assess the sensitivity of 18F‐(‐)‐NCFHEB‐PET to increases in synaptic acetylcholine concentration induced by acetylcholinesterase inhibitors.

Nicotine and Nicotine Abstinence Do Not Interfere with GABAA Receptor Neuroadaptations During Alcohol Abstinence.

BACKGROUND Alcohol dependence and tobacco smoking are highly comorbid, and treating both conditions simultaneously is controversial. Previously, we showed that tobacco smoking interferes with GABAA receptor neuroadaptations during alcohol withdrawal in humans, while this effect did not occur with continued nicotine use during alcohol abstinence in nonhuman primates. Here, we extend our previous work by measuring GABAA receptor availability with positron emission tomography (PET) during drug abstinence in nonhuman primates exposed to alcohol alone, nicotine and alcohol together, and alcohol abstinence with continued nicotine exposure. METHODS Twenty-four adolescent male rhesus macaques orally self-administered alcohol and nicotine, available separately in water and saccharin, over 20 weeks. The groups included alcohol alone (n = 8); nicotine and alcohol with simultaneous abstinence (n = 8); nicotine and alcohol with alcohol abstinence while nicotine was still available (n = 8); and a pilot group of animals consuming nicotine alone (n = 6). Animals were imaged with [(11)C]flumazenil PET to measure binding potential (BPND), an index of GABAA receptor availability. Imaging occurred at baseline (drug-naíve), and following alcohol and/or nicotine cessation at 1 day, 8 days, and 12 weeks of abstinence. Generalized linear mixed models were used to examine the time course of [(11)C]flumazenil BPND during alcohol abstinence across groups. RESULTS Animals consumed 3.95 ± 1.22 g/kg/d alcohol and 55.4 ± 35.1 mg/kg/d nicotine. No significant group effects were observed in [(11)C]flumazenil BPND during alcohol abstinence; however, a main effect of time was detected. Post hoc analyses indicated that all groups abstaining from alcohol exhibited significantly increased GABAA receptor availability at 1 day and 8 days (but not 12 weeks) of abstinence relative to baseline, while no changes in [(11)C]flumazenil BPND during nicotine abstinence alone were observed. CONCLUSIONS These data indicate that neither nicotine nor nicotine abstinence interferes with GABAA receptor neuroadaptations during alcohol withdrawal. This conclusion is consistent with our previous study and does not contradict the use of nicotine replacement therapies or non-nicotinic-acting pharmaceuticals to quit smoking during alcohol withdrawal from a GABAergic perspective.